1. Field of the Invention
The present invention relates generally to scanning probe microscopy and in particular to micromachined submicrometer photodiodes for nanometer scale, near-field photodetection optical microscopy. The invention further relates to a process of fabricating the photodiodes utilizing a novel method of forming small openings in a deposited layer on the end of the micromachined tips of the photodiodes. In addition, the invention also relates to optical intensity mapping on the nanometer scale using the photodiodes in near-field photodetection optical microscopy.
2. State of the Art
In recent years there has been a multitude of developments in scanning probe microscopy that allow imaging on a nanometer scale, yet chemical and molecular identification with these probes remains a great challenge. Standard optical spectroscopic techniques provide a powerful tool for chemical identification but lack spatial resolution on this scale. Near-field optical microscopy offers the possibility of routinely extending the spatial resolution of optical spectroscopy into the nanometer scale. Near-field scanning optical microscopy is an established technique based on the collection or transmission of light through a subwavelength aperture scanned near a surface. Near-field photodetection optical microscopy utilizes a photodetector of subwavelength dimensions. The localized photodetector probe is brought near an illuminated surface where it can directly absorb optical power. As it is raster scanned across the surface the photocurrent signal is recorded to create a two-dimensional image of the optical intensity distribution. The small detector is necessary to achieve a high spatial resolution.
Line photodetectors and light sources that are small (submicrometer) in two dimensions have previously been constructed.